Mitsubishi Process Description

Many different methods are employed in the extraction of copper from sulphide ores. The Mitsubishi Process allows the direct production of copper blister, and has been practiced at the Kidd copper smelter in Timmins, Ontario (shown below) since 1981. It is also used in Naoshima, Japan; Onsan, Korea; Port Kembla, Australia; and Gresik, Indonesia.

Sulphide copper ores are normally treated in two stages: the matte making stage, in which matte and slag are produced by smelting; and the converting stage, in which iron and sulphur in matte are progressively oxidised for the production of blister copper. Although the chemical reactions in both process steps are oxidations, there is a significant difference in the partial oxygen pressure employed. The smelting stage is less oxidising to ensure higher copper recovery, while the converting stage is more oxidising so that residual iron and sulphur is removed.

These two quite distinct reaction conditions are most efficient when each stage is performed in separate furnaces. The Mitsubishi process is therefore a three- furnace system comprising continuous smelting, slag cleaning, and converting. An anode casting stage is then used to produce copper anodes.

The Mitsubishi process is distinct from conventional smelting methods in that the matte grade can be quickly raised to 65-70% copper while maintaining a low level of copper loss in the discard slag. At converting a limestone flux is introduced. This collects oxidised iron (magnetite) effectively and results in a very small tonnage of converter slag. This is readily water-granulated and recycled to the smelting furnace.

Since the three furnaces are stationary, good roof design and small furnace outlets ensure complete off-gas capture. In this way the expensive and difficult to maintain hooding systems used on most rotary furnaces are eliminated.

The molten materials exit the furnaces either by continuous overflow or by syphon, and are conveyed by gravity to the next furnace by sloping launders. This entirely eliminates ladles, fugitive ladle gases, overhead cranes, and ladle skulls.

Each furnace in the three-furnace system can be regarded as a "steady state" reactor. The bathline within each furnace is constant (no tapping), simplifying refractory design and brick cooling.

Process control holds the matte grade steady and ensures optimum operating conditions right through to continuous blister delivery to the anode furnaces.

Anode casting can be by "wheel" or by twin-belt Hazelett caster. The latter is preferred for casting rates approaching 100 tonnes/hour with the continuous nature of the Mitsubishi Process.

Flow-Sheet: The flow-sheet for the Mitsubishi Process is also available. In addition, some information about copper is online, including background and end uses.

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